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(IJSE) Simulation of Traffic Flow Model with Traffic Controller Boundary Internat. J. of Sci. and Eng., Vol. 5(x)2013:xx-xx, xxxx 2013, Nahid Sultana et al. International Journal of Science and Engineering (IJSE) Home page: http://ejournal.undip.ac.id/index.php/ijse Simulation of Traffic Flow Model with Traffic Controller Boundary Nahid Sultana1, Masuma Parvin2, Ronobir Sarker3, Laek Sazzad Andallah4 1Bangladesh University, Dhaka, Bangladesh, Email: [email protected] 2 Daffodil International University, Dhaka, Bangladesh, E-mail: [email protected] 3Bangladesh University of Business and Technology, Dhaka, Bangladesh, E-mail: [email protected] 4Jahangirnagar University, Savar, Dhaka, Bangladesh, E-mail: [email protected] ABSTRACT- This paper considers a fluid dynamic traffic flow model appended with a closure linear velocity-density relationship which provides a first order hyperbolic partial differential equation (PDE) and is treated as an initial boundary value problem (IBVP). We consider the boundary value in such a way that one side of highway treat like there is a traffic controller at that point. We present the analytic solution of the traffic flow model as a Cauchy problem. A numerical simulation of the traffic flow model (IBVP) is performed based on a finite difference scheme for the model with two sided boundary conditions and a suitable numerical scheme for this is the Lax-Friedrichs scheme. Solution figure from our scheme indicates a desired result that amplitude and frequency of cars density and velocity reduces as time grows. Also at traffic controller point, velocity and density values change as desired manner. In further, we also want to introduce anisotropic behavior of cars(to get more realistic picture) which has not been considered here. Keywords - tensity function; tinite difference scheme; macroscopic traffic flow model; nonlinear velocity; tumerical simulation. Submission: March 12, 2013 Corrected : June 20, 2013 Accepted: June 23, 2013 Doi: 10.12777/ijse.x.x.xx-xx [How to cite this article: Sultana, N., Parvin, M. , Sarker, R., Andallah, L.S. (2013). Simulation of Traffic Flow Model with Traffic Controller Boundary. International Journal of Science and Engineering, 5(1),6-11. Doi: 10.12777/ijse.x.x.xx-xx ] I. INTRODUCTION and backward, depending on vehicle density in a given At present time we cannot deal our life not a single area. day without vehicles likes bus, car, taxi, rickshaw etc. for In the fluid flow analogy, the traffic stream is treated our communication. So traffic flow and congestion is as a one dimensional compressible flow. This leads to related to our transportation. At this time traffic two basic assumptions :( a) traffic flow is conserved and congestion is one of the vital problems in our country b) there is a one-to-one relationship between speed and like other developing countries of the globe. density or between flow and density. As mentioned by In mathematics traffic flow is the study of interactions (Daganzo1995), the difference between traffic and fluid between vehicles, drivers, and infrastructure (including as follows: A fluid particle responds to the stimulus from highways, signage, and traffic control devices), with the the front and from behind, however a vehicle is an aim of understanding and developing an optimal road anisotropic particle that mostly responds to frontal network with efficient movement of traffic and minimal stimulus. Many research groups are involved in dealing traffic congestion problems. with the problem with different kinds of traffic models Traffic Phenomena are complex and nonlinear, like the Microscopic car following model, the depending on the interactions of a large number of macroscopic fluid dynamic model and The Mesoscopic vehicles. Due to the individual reactions of human (Kinetic) model. All models describe various situations drivers, vehicles do not interact simply following the with different assumptions and simplifications. In this laws of mechanics, but rather show phenomena of cluster paper, we attention on macroscopic fluid dynamics formation and shock wave propagation, both forward xx © IJSE – ISSN: 2086-5023, xxxxxxxx 2013, All rights reserved Internat. J. of Sci. and Eng., Vol. 5(x)2013:xx-xx, xxxx 2013, Nahid Sultana et al. model because it is more efficient and easy to implement interaction of many vehicles by discussing the than other modeling approaches. fundamental traffic variables like density, velocity and The macroscopic traffic model was first developed by flow. In particular, a linear velocity-density relationship Lighthill and Whitham (1955) and Richard (1956). This which yields a quadratic flux-density relation yields a model is also shortly called LWR. According this model, formulation of traffic problem as a first order non-linear vehicles in traffic flow are considered as particles in fluid; partial differential equation. The exact solution of the further the behavior of traffic flow is described by the nonlinear PDE as a Cauchy problem is presented. method of fluid dynamics and formulated by hyperbolic Moreover, in order to incorporate initial and boundary partial differential equation. This model is used to study data, the non-linear first order (PDE) is appended by traffic flow by collective variables such as traffic flow rate initial and boundary value which leads to formulate an (flux) q(x,t) , traffic speed v(x,t) and traffic density initial boundary value problem (IBVP).Certainly, a numerical method is needed for the numerical r(x,t) , all of which are functions of space, xÎ R and implementation of the IBVP in practical situation and it is time t Î R + . The most well-known LWR model is completely unavoidable to use numerical method to formulated by the conservation equation solve real traffic problem. A numerical scheme for the ¶r ¶q(r ) model which is applicable for any velocity density model + = 0 including discontinuous one is presented in (Kuhne et al., ¶t ¶x 1997). But in this scheme two sided boundary condition The problem of computer simulation techniques of is needed and the accuracy of the scheme is not the traffic flow models has become an interesting area in satisfactory. However, there is a requirement of using the field of numerical solution methods for several one sided boundary condition. In (Andallah et al., 2009) decades. For instance, in (Daganzo1995) the author author considers explicit upwind difference scheme for shows that if the kinematics wave model of freeway traffic model where he considers one sided boundary traffic flow in its general form is approximated by a condition. In this paper first, we present the derivation of particular type of finite difference equation, the finite the macroscopic traffic flow model with corresponding difference results converge to the kinematics wave variables relationship among velocity, flux and density. solution despite the existence of shocks in the latter. Then, we present the analytic solution of the traffic flow Errors are shown to be approximately proportional to model with linear and nonlinear partial differential the mesh spacing with a co-efficient of proportionality equation (PDE) by the method of characteristics and the that depends on the wave speed, on its rate of change existence and uniqueness of the analytic solution of the with density and on the slope and curvature of the initial traffic flow model. We develop a finite difference scheme density profile. The asymptotic errors are smaller than for our traffic flow model as an (IBVP) which has been those of Lax’s first order, centered difference method presented before numerical simulation section. We which is also convergent. In the paper (Zhang 2001) the develop computer programming code for the author develops a finite difference scheme for non- implementation of the numerical scheme and perform equilibrium traffic flow model. numerical experiments in order to verify some This scheme is an extension of Godunov’s scheme qualitative traffic flow behavior for various traffic (Randall .J .Leveque, 1992) to system. It utilizes the parameters. Finally, we present the numerical solutions of a series of Riemann problems at cell simulation. boundaries to construct approximate solutions of the non-equilibrium traffic flow model under general initial II. MACROSCOPIC TRAFFIC FLOW MODEL conditions. Moreover, the Riemann solutions at both left (upstream) and right (downstream) boundaries of a We present an outline of mathematical modeling, a highway allow the specification of correct boundary partial differential equation as a mathematical model for conditions using state variables (e.g. density and / or traffic flow. Also we represent specific speed-density speed) rather than fluxes. Preliminary numerical results relationship and specific flow-density relationship and indicate that the finite difference scheme correctly the well-known LWR model (Haberman, 1977 and Klar et computes entropy-satisfying weak solutions of the al., 1996) based on the principle of mass conservation. original model. In Bretti et al. (2007) the authors We assume all cars have some constant velocity v > 0. consider a mathematical model for fluid dynamic flows Then from the relationship among velocity, flux and on networks which is based on conservation laws. The density, the flux q = rv yields the equation of approximation of scalar conservation laws along arcs is ¶r ¶q carried out by using conservative methods, such as the continuity + = 0 in the form classical Godunov scheme and the more recent discrete ¶t ¶x velocities kinetic schemes with the use of suitable ¶r ¶r boundary
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